Angioplasty has gained wide acceptance in recent years as an efficient and effective method for treating certain types of vascular diseases. In particular, angioplasty is widely used for opening of stenoses in the coronary arteries, although it is also used for treatment of stenoses in other parts of the vascular system. Treatment and opening of the stenosis is effected by maneuvering a catheter having an inflatable balloon area near its tip through the vascular system to position the inflatable balloon at the site of the stenosis. The balloon is then inflated to cause stretching of the artery and pressing of the lesion into the artery wall to reestablish acceptable blood flow to the artery.
Guide wires are often used for establishing the path to the stenosis so that the dilating catheter can subsequently be positioned. In percutaneous transluminal coronary angioplasty (PTCA), a steerable guide wire and PTCA catheter may be introduced into the vascular system at a site remote from the stenosis through a guiding catheter and delivered to either the left or right coronary ostia (entrance to the left and right coronary artery) by that guiding catheter. The guide wire is then maneuvered into the branch of the coronary artery for which treatment is intended. After the guide wire has been advanced past the lesion to be treated, the PTCA catheter is then positioned with its hollow central lumen at the distal tip over the end of the guide wire which is outside the body. With the guide wire held in place, the dilating catheter is then advanced over the guide wire to bring the inflatable balloon portion to the lesion. Thereafter, fluid pressure is applied through external apparatus connected to the catheter to inflate the balloon.
Various problems may be encountered in the above-described angioplasty procedure. One problem which occurs in the case of very tight stenoses with small openings is the inability to advance the dilating catheter across the stenosis after the guide wire has been successfully positioned. Since the tip of the dilating catheter has a significantly greater diameter than the guide wire, there is a practical limit to treatment of such small, tight stenoses using transluminal catheters. Efforts to reduce the diameter of the transluminal catheter are limited by the size of the guide wire. Since a clearance is required to allow the guide wire to pass with relatively minimal frictional resistance, one lumen of the transluminal design must have a diameter of at least 0.002 inch greater than the guide wire to be functional. Guide wires are available in sizes ranging from 0.012 inch to 0.018 inch in diameter. Reduced diameter guide wires have less axial strength, which may make them subject to buckling as they are being advanced, and reduced torsional stiffness, which makes them more difficult to steer and control during insertion. In addition, very small diameter guide wires might under some circumstances create a risk of injury to the blood vessels because the applied axial force is concentrated over a small tip area, which could create a risk of puncturing the artery and creating false lumens. The standard PTCA catheter, which is passed over the guide wire, is limited in size by the need to allow adequate diametral clearance between the guide wire and the inner diameter of the PTCA through channel.
Another device used in coronary angioplasty is a catheter in which a balloon is installed on a wire with a spring tip. This type of catheter offers slightly lower profiles than a transluminal design, but unlike the transluminal design cannot be used in conjunction with a conventional guide wire. Like a standard guide wire, the tips of these catheters are shaped in order to try to navigate the path from the right or left ostia to and past the vessel to be treated. The primary difficulty associated with this type of device is the inability to duplicate the performances of conventional guide wires, particularly the torsional and axial stiffness, as well as the tip flexibility and smoothness of wire transition from the core to the tip safety wire (which secures the spring tip). The second drawback of this type of device is the fact that when catheter balloon size changes are required because of the extreme difficulty of accurately estimating the artery and occlusion sizes, the entire coronary arterial path must be renegotiated with the next catheter since no guide wire is in place reserving an easily renegotiated path. Once the path has been established, it is highly desirable that the path be maintained, yet the use of single lumen systems requires loss and reestablishment of the the path.
Because of these and other problems as outlined above, there is still a need in the field of angioplasty for effective treatment of very tight stenoses with very small openings which cannot be crossed by present angioplasty catheters. Of course, it is highly desirable to be able to treat small stenoses through percutaneous coronary angioplasty techniques, since the alternative is surgical bypass grafting techniques.